Apart from the anosmia there is no difference between Kallmann syndrome and hypogonadotropic hypogonadism.

 Kallmann syndrome (KS) is a type of hypogonadotropic hypogonadism (HH). 

KS / HH is normally present from birth, known as congenital, in which case puberty will be affected or not even start.

HH (but not KS) can occur later in life, after normal puberty, known as acquired HH.